In the above-noted copending application, advantageous properties for new and novel coated abrasive products having backings reinforced with arrays of coplanar and coparallel textile yarns were disclosed. As stated in that application, it is possible to make coated abrasives which are satisfactory for many purposes by combining the use of reinforcing yarn arrays with cloth finishing adhesives used for conventional commercial coated abrasives. Examples of such commercially known adhesives include, for example, water-based phenolic resins, starch, animal hide glue, and a variety of water-borne synthetic organic materials such as polymers of esters of acrylic acid, of butadiene and styrene, or of ethylene and vinyl acetate. However, in some very demanding industrial applications such as heavy duty snagging, I have found the need to use special saturation materials in conjunction with the backings described in Ser. No. 6/280,040 in order to improve the performance of the coated abrasive.
One characteristic of the continuous filament polyester yarn reinforced coated abrasives finished with water based phenol- or resorcinol-formaldehyde adhesives is the generation of large volumes of fuzzy detritus from wear along the edges of the belts. The water based phenol- or resorcinol-formaldehyde resin adhesives apparently do not thoroughly penetrate the interior of the multifilament yarns, although they do encase the yarns. As a result, the interior filaments of the yarns are relatively poorly bonded into the structure of the coated abrasive after the surface encasement of resin is broken, as it often is, either by slitting wide abrasive webs to make belts of a desired narrower width or by wear along the edges of belts during use. Poorly bonded interior filaments thus exposed are easily pulled out of the belt, often in fluffy form which occupies a sufficient volume to cause nuisance to the operator using the belt.
Coated abrasive belts having filament polyester reinforcing yarns or woven polyester fabrics that contain substantial amounts of filament yarns and are finished with conventional adhesives containing phenol- or resorcinol-formaldehyde occasionally experienced splitting and/or excessive elongation under the stres of grinding. In addition, laboratory measured tests for tear strength and resistance to elongation (particularly under forces in excess of 25 dekanewtons (daN) per 25 cm of width) coated with conventional adhesives containing phenol- or resorcinol-formaldehyde have indicated a need for improvement in these characteristics for the industrial applications involving aggravated snagging conditions.
It is hypothesized that the reason for all the phenomenon noted above is the relative difficulty of penetration of the multifilament yarns by the adhesives used. Phenol-formaldehyde and resorcinol-formaldehyde adhesives after cure have very high heat distortion resistance, which is a valuable property for coated abrasives, but like all other water-based adhesives, they are relatively poor at wetting the basically hydrophobic surfaces of polyester filaments and thus at penetrating into yarns with many filaments. Better overall bonding, however, appears to be achieved when the yarn consists of many short lengths of fine filaments as in staple rather than very long larger filaments as in multifilament, probably because of the greater surface area of polyester per unit area of fabric surface in the former case. A special object of this invention is to provide finishing adhesives which under practical processing conditions will bond sufficiently to multifilament polyester yarns so as to produce coated abrasive products, coated on backings reinforced with such multifilament yarns, which will be at least as resistant to elongation, splitting, and fuzz generation during use as are conventional coated abrasives with woven staple polyester cloth which is finished with phenol-formaldehyde or resorcinol-formaldehyde resins. Other objects will be apparent from the disclosures below.